2

The problem

I have a Volkswagen Transporter T4 with an 02b gearbox. It's very similar to the normal water-cooled VW manual (e.g. 02a and 02j) gearboxes.

It has begun to be intermittently difficult to shift into gear. It does not make any strange noises, such as a bearing whine.

The weird symptom

Engine running, when I put the car in neutral it will roll freely on a slight grade. Pressing the clutch and pushing it into gear (especially first) causes it to stop rolling as the synchro bites. To be extremely clear, this is all done while the engine is running, not stopped.

Why?

The input shaft must be significantly slowed somehow so that when the output synchro begins to press into the gear it acts like a brake. What reasons could cause this?

Update

I experimented with it again tonight. Driving ~50 mph and shifting into 1st slowly (clutch depressed of course) does make it audibly whine once in gear. You can hear the input shaft spinning up as the synchro grabs before it finally goes into gear. Interestingly enough, it shifted smoother after this for a short while. Shifting into first, engine off, clutch depressed (and not released) during a slow roll also makes soft but expensive noises that sound like the drivetrain rocking against its mounts. I'm going to pull the transmission as soon as my schedule allows, but I suspect input shaft bearings.

1

The clutch is not fully releasing.

When you press the clutch pedal to the floor, the clutch should disengage. The symptoms you report suggest that the clutch is only partially disengaging (you can shift into a gear), but not fully disengaging (when you get into a gear, the car behaves as if the brakes were being applied).

I am unfamiliar with the VW Transporter T4, and so cannot advise you further. If this is a hydraulic clutch, either the master or the slave cylinder could be failing. If the clutch is operated mechanically (by rod, or cable), check its adjustment — too little play in the system could result in the same not-quite-disengaged state.

  • Thanks for the input! I would agree and expect the car to brake if the engine was off when doing this test. And at first, it was, and it did seem like the clutch was dragging. But with the engine running it behaves the same way— clutch in, neutral: it rolls; clutch still in, in gear: it slows and stops. If the clutch were dragging I would expect it to grind, then roll faster, not stop. – adc Jul 10 at 2:20
  • @adc Well...something's wrong in there. If the clutch linkage/hydraulics are OK externally, then you're going to have to separate the gearbox from the engine in order to go further. Something, or some combination of things, is awry at or within the clutch, or internally in the gearbox. – DavidSupportsMonica Jul 10 at 2:24
1

Just sounds like your clutch needs to be adjusted, like it isn't disengaging fully when fully depressed leading to being locked up when in gear.

If its behaving differently when the engine is running it could just be because the engine torque is enough to overcome some amount of friction and causes the clutch to begin slipping. Once slipping I imagine it has a much easier time of keeping that going due to dynamic friction being different to the static friction.

  • The behavior is noted with the engine running, but the same thing happens with the engine off. It's a hydraulic clutch with no adjustment. – adc Jul 10 at 7:15
  • 🤦‍♂️I forget cars don't have clutch adjustment. I had a bit of a look and found a similar sounding issue here: vwt4forum.co.uk/archive/index.php/t-114189.html one interesting thing from that was "A common casue for T4 biting point issues and a dragging clutch with the 02b gearbox is that the fulcrum point collapses within the bellhousing.The pivot for the fulcrum point has a red plastic cap over the steel post and what happens particularly with high mileage T4s is the plastic cap breaks up resulting in the steel post wearing through the clutch lever and upsetting the angles..." – Tom H Jul 10 at 7:33
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Cause

I had several work related delays but removed the transmission and split the case. From there it was apparent that the third gear on the pinion shaft did not rotate freely. It was not locked to the shaft, but there was significant friction (I could not rotate it by hand).

The reason this manifested in the car slowing as soon as it was shifted into gear (despite the clutch pedal being pressed) is because it was effectively 90% of the way in third gear at all times. With the selector in neutral, the pinion shaft was driven through third gear. This spun the input shaft normally through its input third gear. Shifting into any other gear, however, did not remove this third-gear friction, but additionally locked another gear pair (e.g. second gear) to the pinion shaft. Since the pinion shaft cannot drive the input shaft at both the third and second gear ratios at the same time, one was forced to give. Third gear would then slip, second gear would work correctly, but the friction on the pinion shaft would work to slow the car.

A similar effect during normal gear shifting caused the input shaft to be driven at third gear speed as soon as the transmission passed through neutral. This made shifts extremely difficult, usually grinding no matter how slow and deliberate.


Solution

After pressing off the gears, I was surprised to find the needle bearing (29) and race in great shape. However, the spring clips (33) that hold the "dogs" (synchronizer ring indexing pins, 20 in the figure below) to the shift collar were both broken. I believe they were wedged between the third gear synchro and the 3/4 shift collar, preventing the gear from spinning. The synchro ring looked good.

VW Transporter 02B Transmission Shafts

I replaced the spring clips, the third gear needle bearing (since I'd bought the part and it was a revised design), and pressed the shaft back together. All gears now work as expected.

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